Transformer



Nov. 14, 1939. FjMccURTAIN 2,179,795

IN VEN TUR Nov. 14, 1939. F. MccURTAlN j 2,179,795

TRANSFORMER Filed Mar'cn 1o, 1957 2 sheets-sheet 2 1N VEN rok atentecl Nov. '14, 1939 UNITED STATES Whittie PATENT TRANSFORMER Application March 10, 1937, Serial No. i3,l79

' 1 claim. (ci. 1v1- 119) This invention relates to a high reactance ansformer for the supply oi current to current zsponsive devices of unstable nature. Typical f such loads are the gaseous conduction lighting ibes, in which connection the invention is illusrated herein in its preferred embodiments. It ray, however, be adapted to and used in con- .ection with electric Welding and various other )ads of the variable resistance type.

The main object or the invention is to provide transformer suitable ior delivering current to .nstable load devices, the mean value of which urrent may be controlled over a wide range of alues. In connection with gaseous conduction lghting tubes, this implies that the transformer vill develop on each current pulse a voltage suficient to break down the resistance of the gas olumn regardless of the mean current ow, the nean current ow being independent of this iniial voltage and depending on the transformer .djustment.

Various attempts have been made to produce a `ransformer suitable for lighting gaseous dis- :harge tubes to variable and controlled intensity. i need exists for such a device for stage lighting, lisplay and general illumination comparable to ,he uses of dimming with incandescent lamps.

Adaptation of the typical high reactance trans- :'ormer of the discharge tube lighting art have lot been successful for this purpose, which may Je understood from a consideration of the func- ;ion thereof. Such a transformer consists typizally, of a primary and a secondary winding fairly loosely coupled to each other on a core structure in which a high reluctance magnetic shunt bridge provides a path for the nux alternate to that through the secondary winding. Since very little current flows in the secondary before the resistance of the gas column of the load is broken downthere is very little counter motive force developed and consequently the shunt bridge does not materially effect the Voltage across the terminals of the tube. After current flow has been established through the tube, the counter motive force developed by the secondary winding causes a part of the hun to take the path through the shunt bridge, thus restricting the secondary voltage and preventing excessive current new. The transformer in one respect acts as a choke coil. The power factor is necessarily low and a heavy wattless current flows in the primary circuit.

Any impedance inserted in the primary circuit to regulate the mean current value will also interfere with the development of the minimum initial voltage necessary to establish current flow lent Voltage surges and high frequency effects.

Such conditions are highly destructive to the tube electrodes, the insulation and the transformer, and are to be avoided in commercial work.

It has been found also, with this type of installation, that the tendency of the tube to oscillate with its connected apparatus enters as a limiting factor in the design. The typical high reactance shunt bridge transformer has been den veloped to modify the voltage curve within the limitations of several variables. The degree to which the secondary voltage may be reduced through the shunt bridge action is conditioned by the fact that if the voltage is reduced too far, the discharge is unstable and the tube forms an oscillation generator with the transformer.

The use of regulating impedances with transformers properly designed for steady operation results in carrying the operation into the danger range. -To design a transformer of this type for operation in connection with regulating impedances results in bulky and expensive construction. It is an object of this invention to provide a transformer which will develop the minimum striking voltage overa Wide range of mean current values without iiicker or undue high frem quency effects and Without sacrificing the light and efficient construction necessary for commercial purposes.

It is known in the art to construct transformvers having shunt bridgeswith windings thereon, the windings being in series with impedances forming circuits independent of the primary or secondary circuits. In such a transformer, energy is drawn oii in the shunt bridge coil circuit, thus reducing the energy available for the secondary. It has been found that this circuit forms an oscillating couple with respect to the rest of' the device. At come point in the regulation curve a violent oscillation appears and may be strong enough to extinguish the tube. The more loosely coupled the bridge coii is with the primary and secondary, the more definite this eiiect will be. The regulation curve must naturally be limited tor exclude this state ci operation, thus placing a severe limitation on the application of this type @si a of device. lt is an. object of this invention to provide a transformer for this service in which all the windings in forced condition with respent to the impressed voltage and which there are no elements in a state free to set up transfers accordance with any other "le,

N further object oi the invention to elimielements within the 'transformer case which effect regulation of current by consuming energy. @ne important condition in 'transformer design to dissipate the minimum of energy around the windings, 'which object is complied with in accordance with this disclosure. The use of regulating windings within the transformer must always be attended with comparatively A large consumption of energy in such windings and corresponding generation of heat. This heat, by the of the case, is developed the point most clisadvaintageous for transformer operation and must be taken into consideration in the commercial design. .Tri my transformer the windings are not charged with the duty of dissipating any heat other than incidental to the normal currents of this worlr. rthus, transformers made according to my invention may be constructed in the usual manner of gaseous tube lighting trans farmers, sealed in wat: and installed without any special cooling provisions.

Further objects of the invention will become apparent from the following specification in connection with the accompanying drawings.

in the drawings the same numeral is used throughout to indicate the same or equivalent part when found in several views.

Figure l is a diagrammatic representation of a transformer constructed according to this invention, provided with a flashing switch and connected to a gaseous conduction lighting tube load. Figure 2 is a representation of a similar trans former provided with windings on the shunt bridges to accentuate the bridge action.

Figure Si is a diagrammatic representation of a similar transformer modied by the use of a winding on one bridge only and shown connected to an impedance regulator for continuous variation of the tube brilliancy.

.Figure i is a diagrammatic representation of a transformer having a double balanced secondary winding and primary windings moulded accordingly. .Figure is a representation of the same transformer modified by the addition of windings on two of the shunt bridges.

in Figure l I have shown a transformer made according to this invention connected to a gaseous discharge tube. The tube, indicated by lnumeral 2, will be understood to represent any of the various types of glow, vapor arc orl positive column tubes common in the art. The transformer, indicated by numeral l, is shown somewhat diagrammatically, in a fashion conductive to clear representation and without regard to physical proportions or ratio of turns in. the windings.

The core proper consists of the main legs d and 5 and the end bars t and ll, which form a closed magnetic circuit. The structure is formed of C shaped and straight laminations interstacked in the joints and 3i. In practice these laminations will be riveted, bolted or clamped together. On theleg 4 are positioned the primary windings I0 and il and the secondary winding I2. between the windings l0 and l l and provides a path for the ux developed by winding l0 alter- The magnetic shunt bridge i4 is positioned atraveo nate to the path through the secondarywinding. The magnetic shunt bridge l is positioned be tween windings l i and l2 and provides a path for the fluir developed by both pri ary windings alternate to the path through the secondary wind-s ings.

The reluctance of the shunt bridges should be comparatively high as compared with the reluctance of the path through the secondary wind-- ing before current iiow has been. established in the secondary circuit. There are various ways of constructing the bridges. i have represented them as constructed of stacks of iron laminations wedged in between the legs [i and of the core proper and separated therefrom by the non` magnetic blocks iii, il l 'Elue larsl nations may, however, be driven in between the core legs in direct contact therewith and reliance placed ou the nature of the contact thus formed to develop the necessary" reluctance. file laminations may loe riveted together, held by wrapp-ings of insulating paper otherwise bound in a solid sta s. l

IThe terminals and ofthe primary winding l@ are shown connected to the line. The terminal Z5 of the winding il is shown connected through the switch liti to the line, while the other terminal 2li is connected direct to line. Ends and l 'of the secondary winding are shown connected to the tube load. In practice these teru minals are brought out in high tension posts set in the transformer ease. secondary winding may be grounded as indlcated at ld. in practice this is done by grounding the coil to the transformer core and case; it being understood that the case will be connected to ground when installed. y

The elements of this transformer are so proportioned that, when connected to the tube load for which it is designed and the primary winding lil alone is energized, the tube will be lighted in the typical manner to the minimum brilliancy value desired. in this respect the transformer functions in the same manner as the typical shunted bridge transformers of the art, the two bridges in this case acting in the same fashion. V/'hen the primary coil il is also connectedY in circuit the tube will be lighted to the maximum brilliancy' value desired. The tube may be flashed between these two brilliancy values by means of the switch, the coil l@ remaining in circuit continuously.

i prefer to wind both primary coils so that they will be capable separately of developing a voltage in the secondary winding sufficient to ignite the tube. This means that they should have about the sa'me number of turns, although this may be deviated from in certain cases. However, since the primary it in this case is always in circuit during operation, it may be charged with the duty of igniting the tube and the primary Il in response to other demands wound so that it will not, of itself, suice for this duty.

Since there is a greater leakage for magnetic flux for coil lll it may be wound with finer wire than coil l i In the proportioning of the bridges the same general conditions prevail as in the case of the typical shunt bridge transformers of the art. Close coupling between primary and secondary windings makes for denite voltagev rise on each current pulse which is desirable from the viewpoint of ignition of the tube. Leakage through the bridge is desirable from the viewpoint of current regulations. The necessities of insulation also enter the problem by setting cerfir,

The mid point of the 55 develop the minimum igniting tain minimum spacing between primary and secondary winding.

In each type of installation these considerations may be met by a particular selection of design features. However, for loads which have a strong negative resistance behavior, a modification of the invention shown in Figure 2 may be used.- In this view windings are supplied on the shunt bridges. The Winding 33 on bridge I4 is in series with primary winding I0. The winding 32 on bridge I3 is in series with primary winding Il. The function of these windings is to intensify the bridge action and increase the spread between the igniting voltage and the burning voltage of the tube. In the application of this feature, the proportions of the transformer may be altered. The coils-may be much closer coupled and the section of the bridges reduced. This feature is disclosed and claimed in my copending application, Serial No. 78,153, illed May 6, 1936.

A modification of this construction is shown schematically in Figure 3, in which view a transformer is provided with a bridge coil only on the bridge between the coils Il and I2. Inasmuch as this bridge carries the heavier flux, it will suiiice for some purposes to limit the extra winding thereto.

In this view I have shown a variable impedance in place of the switch. ,The choke coil is connected in series with the primary winding Il. It is provided with a movable armature 4| by means of which the intensity of the tube may be continuously varied'between the extreme values. It is to be understood that this type of variable impedance, or any other type, may be substituted for the switch in the various views in the drawings.

While I prefer to construct the transformer so that each primary winding will have suicient turns to develop the minimum striking voltage by itself in the secondary winding, this may be deviated from in certainl cases. One such case is illustrated in Figure 3. The winding I0 may be considered together with the effective phase of winding Il at its lowest adjustment as developing the minimum strihng voltage since the winding II is never completely out of circuit.

In the transformer shown in Figure 4 I have provided a double balanced secondary winding.

The secondary is indicated by the numerals and 46, and consists of two coils separated by the double primary 41 and 43 and the single primary winding 49. 'Ihe primary 49 serves to voltage for both secondary coils. The primary 41 and 48 serves to develop the major current iiow. Four shunt bridges 5U, 5|, 52 and 53 are provided and function in the same fashion as in the previously described transformers.

In Figure 5 I have shown the preferred manner oi' applying shunt bridge windings to the transformer of Figure 4. The windings 54 and 55 are in series with the double primary and correspond in their function to the bridge winding of Figure 3. It is to be understood that the disposition of the bridge coils in all the views may be varied in accordance with the various factors controlling the design of transformers for specific purposes.

Having thus described I ny invention, what I claim is:

Means for selectively controlling the current ,in a load circuit of varying resistance comprising a source of alternating current, a load circuit of varying resistance, a transformer connected between said source of alternating current and said load circuit, said transformer embracing as its essential parts a closed core structure on which are positioned in the order named a single secondary winding which is connectedto said load circuit and two primary windings, both of which are adapted to induce current in said secondary winding, a high reluctance magnetic shunt interposed between said secondary winding and the adjacent primary winding, and a high reluctance magnetic shunt interposed between said primary windings to thereby provide a single shunt around said secondary winding for the flux developed by the adjacent primary winding and parallel shunts around said secondary winding for the flux developed by the primary winding remote from said secondary winding, and one of said primary windings being connected to said source of alternating current and so designed as to send suflicient flux through the core of said secondary winding to cause sufiicient current' to iiow through said secondary winding and consequently through said load circuit to supply a predetermined current to said circuit and means for connecting the other of said primary windings to said source of alternating current, said last mentioned primary winding being so designed as to cooperate with said rst mentioned primary winding to send suflicient additional flux through the coreof said secondary winding to cause a substantial additional current to iiow through said load circuit.

FRANK MOCURTAIN. 

